This invention relates generally to a device for holding soft, pliable objects or materials, and more particularly relates to a medical device for holding soft tissue. The present invention includes a grip having opposed gripping surfaces that contact the soft tissue. The gripping surfaces are cooled to thereby freeze the tissue adjacent the gripping surface. In this manner, the grip may be clamped onto the frozen tissue with an applied load sufficient to hold the tissue within the grip. The frozen tissue withstands the compression forces of the grip without greatly deforming the soft tissue. All the tissue adjacent the gripping surface freezes, thereby distributing the clamping load of the grip equally among the fibers and further reducing potential tissue damage.
In the past, medical devices have been utilized to attempt to hold in place soft pliable tissue. These devices typically include a grip member that clamps, pinches, grasps or otherwise attempts to hold the soft tissue. The grip member of these devices typically only holds in place the outside surface of the soft tissue. Because biological tissue is soft, the central portion of the test sample is not held stationary by the grip member. Further, biological tissue such as skin, muscle, and tendon is commonly very slippery and slips out of the grip members. Also, soft tissue has a very low coefficient of friction, and compression of the tissue causes expression of fluid, which creates a slippery film and further decreases the coefficient of friction for the tissue. Hence, the tissue must be gripped with enough force to avoid slipping between the grip members when a load or force is applied to the tissue in a direction away from the gripping members.
The large compressive forces that are required to grip the tissue without slipping may cause large deformations of the tissue and often results in failure of the tissue at the grip interface. Further, clamping or tightening the grip members may cause damage to the tissue. Grip members with roughened surfaces that rely on large compression forces often sever or otherwise damage some of the fibers in the tissue. Attachment of the tissue to the gripping members with the use of sutures instead of compression devices almost always causes failure of the tissue at the suture site.
Various medical devices have been utilized to test the mechanical properties of a test sample of tissue. This material testing equipment may, for example, typically requires holding the test sample at opposite ends and repeatedly stretching the tissue. Any slipping of the tissue test sample within the grips during testing will affect the accuracy of the test results. Further, if the sample partially fails or is damaged, the accuracy of the results is affected. Also, large deformations of the clamped part of the tissue also cause unequal load distribution among the fibers, leading to unreliable test results.
In an attempt to increase the accuracy of the material testing equipment, the ends of the test sample may be frozen. By freezing the sample when it is lightly clamped between the gripping members and conforming to the surface of the grip, the sample becomes mechanically rigid and stiff enough to prevent the sample from being damaged and also from slipping out of the grip. Since the sample is not frozen over its entire length, freezing the ends of the sample do not typically affect the results of mechanical tests of the test specimen.
In the past, the ends of the test sample have been frozen using a cryogenic material such as liquid carbon dioxide, dry ice or liquid nitrogen. The cryogenic material may be applied to freeze the grip and test sample by, for example, circulating the cryogenic liquid through passages formed in the grip. Typically, only one half of the grip is cooled, requiring adequate insulation of the other side of the grip to avoid at least partial thawing of the test sample. Also, use of cryogenic liquids requires special handling and storage procedures and the cryogenic liquid must be applied continuously to avoid thawing of the sample.
Further, grips cooled with cryogenic liquids are not compatible with environmental chambers used during the testing of biological materials. For example, many biological materials must be tested under biological conditions (37xc2x0 C. and wet) to obtain accurate test results of the sample tissue. Typically, the entire sample and grip are submersed in a saline bath that is maintained at 37xc2x0 C. Grips that use cryogenic liquids to freeze the test sample also freeze the water in the saline bath, or at least make it difficult to maintain the bath at the desired temperature. Additionally, temperature control of these grips requires special valves designed for cryogenic materials. Hence, a need exists for a gripping member that holds the biological tissue and reduces the potential that the test sample will slip within the grip without the use of cryogenic liquids. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.
The present invention is directed to a thermoelectric grip for gripping soft materials including, without limitation tissue, wherein the grip freezes the portion of the tissue that contacts the grip without the use of cryogenic liquids. The thermoelectric grip of the present invention generally includes first and second spaced apart opposing grip members. Each grip member has an outer gripping surface and a thermoelectric cooler adapted for cooling the outer gripping surface. The thermoelectric cooler is isolated electrically from the outer gripping surface. The grip members of the present invention may include actuating members coupled thereto, wherein the actuating members actuate the first and second grips to change a separation distance between the first and second grip members.
In use, the grip members freeze the soft tissue that contacts the outer gripping surface. The entire end of the tissue in contact with the gripping surface may freeze, rather than just an outer portion of the soft tissue. A controller may be electrically coupled to the thermo-electric cooler to control a temperature at the outer gripping surface and the controller may also control a rate of cooling the outer gripping surface. In the preferred embodiment, the outer gripping surface includes a removable jaw plate, wherein the jaw plate includes an outer contoured surface suitable for gripping various sized soft tissue. Those skilled in the art will appreciate that, without limitation, the grip of the present invention may form a gripping end of a forceps, the gripping end of a surgical instrument, or the grip of material testing equipment, to name just a few devices used to grip soft tissue.
The grip of the present invention allows the holding and/or testing of biological tissue without damaging the tissue and without breaking the tissue at the grip site, while also preventing slippage of the tissue out of the grip. The grip also enables accurate testing of biological and soft materials, to accurately determine the properties of the tissue sample. The thermoelectric grip of the present invention may be sized appropriately to work with a wide range of tissue sizes. By making the jaw face of the grip easily replaceable, each grip may be used for many different sample shapes and many different test types.
Those skilled in the art will appreciate that a thermo-electrically cooled grip offers several advantages over cryogenic liquid cooled grips. For example, without limitation, thermoelectric coolers use electricity to generate freezing temperatures, thereby eliminating the need to purchase, handle, and store cryogenic materials. Also, the temperature of the thermoelectric cooler is readily controlled and the zone of cooling may also be controlled. In this manner, the thermo-electric grip of the present invention is suitable for use in a liquid bath without freezing the liquid around the grip. Further, standard temperature controllers may be used to control the temperature of the grip and thus the amount of the tissue that is frozen.
These and other advantages of the present invention will become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment especially when considered in conjunction with the claims and accompanying drawings in which like numerals in the several views refer to corresponding parts.